What are the recommended antibiotic regimens for common gastro infections?

Antibiotic Regimens for Common Gastroenteritis

For acute watery diarrhea in immunocompetent adults, azithromycin 500 mg single dose is the preferred first-line antibiotic, while for febrile diarrhea or dysentery, azithromycin 1000 mg single dose is recommended. 1, 2

Specific Pathogen-Directed Therapy

Shigella Species

• First-line: Fluoroquinolone (ciprofloxacin 500 mg twice daily or levofloxacin 500 mg once daily for 3 days) 1
• Alternative: Azithromycin 500 mg once daily (effective alternative given increasing fluoroquinolone resistance) 1
• If susceptible: TMP-SMZ 160/800 mg twice daily for 3 days 1
• Immunocompromised patients: Extend treatment to 7-10 days 1

Salmonella (Non-typhoidal)

• Routine treatment NOT recommended for uncomplicated cases in immunocompetent patients 1
• Treatment indicated if: Age <6 months or >50 years, prosthetic devices, valvular heart disease, severe atherosclerosis, malignancy, uremia, or immunocompromised state 1
• Preferred regimen: Ciprofloxacin 500 mg twice daily for 5-7 days (if susceptible) 1
• Alternatives: TMP-SMZ 160/800 mg twice daily or amoxicillin 500 mg three times daily (based on susceptibility) 1
• For bacteremia: Ceftriaxone 2 g once daily PLUS ciprofloxacin 500 mg twice daily initially, then de-escalate based on susceptibility 1
• Immunocompromised patients: Extend treatment to 14 days or longer if relapsing 1

Campylobacter Species

• First-line: Azithromycin 500 mg once daily for 5 days (preferred due to 19% fluoroquinolone resistance) 1, 2
• Alternative: Fluoroquinolone (ciprofloxacin 500 mg twice daily for 3 days) only in areas with low resistance 1

Yersinia Species

• Mild cases: Antibiotics usually NOT required 1
• Severe disease or immunocompromised: Fluoroquinolone (ciprofloxacin 500 mg twice daily) OR TMP-SMZ 160/800 mg twice daily OR doxycycline 100 mg twice daily 1
• For bacteremia: Ceftriaxone 2 g once daily PLUS gentamicin 5 mg/kg once daily 1

Enterotoxigenic E. coli (ETEC)

• Preferred: Azithromycin 500 mg single dose 2
• Alternatives: Ciprofloxacin 750 mg single dose OR levofloxacin 500 mg single dose (if susceptible) 1, 2
• Another option: Rifaximin 200 mg three times daily for 3 days (only for non-invasive illness) 2

Enterohemorrhagic E. coli (STEC/EHEC)

• AVOID antibiotics - may increase risk of hemolytic uremic syndrome 1
• AVOID antimotility agents 1

Vibrio cholerae

• Single-dose options: Doxycycline 300 mg OR azithromycin 1000 mg OR fluoroquinolone (ciprofloxacin 1000 mg) 1
• Multi-day option: Tetracycline 500 mg four times daily for 3 days 1

Clostridium difficile

• Non-severe CDI: Metronidazole 400-500 mg three times daily for 10 days OR vancomycin 125 mg four times daily for 10 days OR fidaxomicin 200 mg twice daily for 10 days 1
• Severe CDI: Vancomycin 125 mg four times daily for 10 days OR fidaxomicin 200 mg twice daily for 10 days 1
• If oral administration not possible: Metronidazole 500 mg three times daily IV for 10 days, consider adding vancomycin 500 mg via nasogastric tube or rectal enema 1

Parasitic Infections

Giardia

• Metronidazole 250-750 mg three times daily for 7-10 days 1

Cryptosporidium

• Immunocompetent: Consider paromomycin 500 mg three times daily for 7 days only if severe 1
• Immunocompromised: Paromomycin 500 mg three times daily for 14-28 days, then twice daily if needed 1

Cyclospora

• TMP-SMZ 160/800 mg twice daily for 7 days (immunocompetent) or four times daily for 10 days followed by thrice weekly indefinitely (immunocompromised) 1

Entamoeba histolytica

• Metronidazole 750 mg three times daily for 5-10 days PLUS either diiodohydroxyquin 650 mg three times daily for 20 days OR paromomycin 500 mg three times daily for 7 days 1

Complicated Intra-Abdominal Infections

Community-Acquired, Mild-to-Moderate Severity

• Single agents: Ertapenem 1 g daily, moxifloxacin 400 mg daily, tigecycline 100 mg loading then 50 mg every 12 hours, cefoxitin 2 g every 6 hours, or ticarcillin-clavulanate 3.1 g every 6 hours 1
• Combination regimens: Cefazolin 1-2 g every 8 hours, cefuroxime 1.5 g every 8 hours, ceftriaxone 1-2 g every 12-24 hours, cefotaxime 1-2 g every 6-8 hours, ciprofloxacin 400 mg every 12 hours, or levofloxacin 750 mg daily—each PLUS metronidazole 500 mg every 8-12 hours 1

High-Risk or Severe Community-Acquired

• Single agents: Imipenem-cilastatin 500 mg every 6 hours or 1 g every 8 hours, meropenem 1 g every 8 hours, doripenem 500 mg every 8 hours, or piperacillin-tazobactam 3.375 g every 6 hours 1
• Combination regimens: Cefepime 2 g every 8-12 hours, ceftazidime 2 g every 8 hours, ciprofloxacin 400 mg every 12 hours, or levofloxacin 750 mg daily—each PLUS metronidazole 500 mg every 8-12 hours 1

Intra-Abdominal Sepsis

• Preferred first-line: Meropenem 1 g IV every 6 hours by extended infusion 3
• Alternatives for septic shock: Doripenem 500 mg IV every 8 hours by extended infusion OR imipenem-cilastatin 500 mg IV every 6 hours by extended infusion 3
• For beta-lactam allergy: Eravacycline 1 mg/kg IV every 12 hours OR tigecycline 100 mg IV loading dose, then 50 mg IV every 12 hours 3

Duration of Therapy

Gastroenteritis

• Most bacterial gastroenteritis: 3-5 days 1, 2
• Severe infections or immunocompromised: May require 7-10 days or longer 1

Intra-Abdominal Infections

• Standard duration: 4-7 days with adequate source control 1, 3
• Immunocompromised or critically ill: Up to 7 days based on clinical conditions and inflammatory markers 3
• Continue until: Resolution of fever, normalization of WBC count, and return of gastrointestinal function 1

Critical Considerations and Common Pitfalls

Fluoroquinolone Resistance

• Increasing resistance in E. coli (up to 20%) - review local susceptibility patterns before prescribing 1
• Campylobacter resistance to fluoroquinolones is 19% - azithromycin is now preferred 1, 2

When NOT to Treat

• Non-typhoidal Salmonella in healthy adults - treatment may prolong carrier state 1
• Enterohemorrhagic E. coli (STEC) - antibiotics may precipitate hemolytic uremic syndrome 1
• Mild Yersinia infections - typically self-limited 1

Adjunctive Therapy

• Loperamide with antibiotics reduces symptom duration in acute watery diarrhea but should be avoided in dysentery or febrile illness 2
• Source control is paramount for intra-abdominal infections - surgical intervention or drainage should not be delayed 3

Culture Considerations

• Obtain cultures within 72 hours of hospital admission for community-acquired pathogens (Salmonella, Shigella, Yersinia, Campylobacter) 1
• Routine cultures optional for low-risk community-acquired infections but valuable for epidemiological surveillance 1
• Mandatory cultures for high-risk patients, health care-associated infections, or when local resistance exceeds 10-20% 1

Delaying Treatment

• Delaying appropriate antimicrobial therapy increases mortality, reoperation rates, and hospitalization duration - initiate empiric therapy promptly in severe cases 3